Forced air flow air-heating furnace



Nov. 24, 1953 H. s. MURPHY 2,660,160

FORCED AIR LOW AIR-HEATING FURNACE Filed Oct. 12, 1950 5 Sheets-Sheet l I v INVENTOR flii'orweys.

1953 H, s. MURPHY 2,660,160

FORCED AIR FLOW AIR-HEATING FURNACE Filed Oct. 12, 1950 3 Sheets-Sheet 2 INVENTOR.

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Nov. 24, 1953 H. S. MURPHY FORCED AIR FLOW AIR-HEATING FURNACE! 3 Sheets$heet 3 Filed Oct. 12, 1950 w T w W.

Patented Nov. 24, 19 3 UNITED STATES PATENT OFFICE FORCED AIR FLOW AIR-HEATIN G FURNACE Harry S. Murphy, Bulfalo, N. Y.

Application October 12, 1950, Serial No. 189,703

2 Claims. I

This invention relates to a hot air furnace and more particularly to a domestic hot air furnace through which the air to be heated is propelled by a blower.

One of the principal objects of the invention is to, provide such a hot air furnace which is very compact considering its capacity and which at the same time does not impose a high back pressure on the blower.

A further object is to provide a way when a part of the air, under control, is propelled at high velocity through restricted passages or tubes crossing the combustion chamber and in which this effect is achieved without undue back pressure on the relatively low pressure blower.

Another object is to decrease the number of square feet of heating surface by increasing the transmission rate of the heat transfer surfaces due to a high velocity of the air through the tubes.

Another object is to provide such a hot air furnace which has low impedance to the flow of air being heated and which will thereby handle a large volume of air.

Another object is to provide such a hot air furnace which is rapid in its response and will quickly bring the air stream up to the desired temperature.

Another object is to provide such a hot air furnace in which the air from the relatively low pressure blower is entrained to provide the high inlet pressure necessary for such high speed movement of the air through the passages or tubes, when tubes are used, without imposing undue back pressure on the relatively low pressure blower.

Another object is to provide such a hot air furnace in which, particularly due to the high air speed through the passages or tubes, there is a high rate of heat transfer from the products of combustion to the air with a correspondingly low flue gas temperature and high efficiency.

Another object is to provide such a hot air furnace in which all parts of the combustion chamber walls are maintained within safe operating temperatures so that the combustion chamber will not burn out, particularly at any one place subjected to excessive temperatures.

' Another object is to provide such a hot air furnace, which for its capacity, is very low in weight.

Another object is to provide such a hot air furnace which can be used to obtain any desired leaving air temperature.

Other objects and advantages of the invention will beapparent from the following description and drawings in which:

Fig. l is a vertical fore-and-aft section through a hot air furnace embodying the present invention.

Figs. 2, 3 and 4 are vertical cross sectional views, on a reduced scale, taken on the correspondingly numbered lines on Fig. 1.

Fig. 5 is a fragmentary section similar to Fig. 1 with the combustion chamber in elevation and showing a modified form of the invention.

Fig. 6 is a vertical section taken on line 6-6, Fig. 5.

The hot air furnace is shown as contained within a vertically elongated generally rectangular casing or housing I0 having a bottom wall II, a front wall I2, a rear wall I3, side walls I4 and a top wall I5.

The casing is divided by a vertical central transverse partition I6 into two chambers I! and I8, the chamber I'I containing a motor driven blower indicated generally at I9, and the chamber I6 containing a combustion chamber shell indicated generally at 20.

The chamber I? is shown as having an air inlet 2I through its top wall I5, and an air filter 22 of any suitable form extending across the upper end of this chamber I I so that the air drawn into the furnace is filtered. This air is drawn in by the motor driven fan unit I9 which is shown as comprising a scroll or volute fan housing 23 having a pair of opposite air inlets or eyes 24 concentric with its fan shaft 25. This fan shaft is shown as having fastened thereto a pulley 26 driven through a belt 28 from the pulley 29 on the shaft 30 of an electric motor 3 I, this motor 3| being shown as suitably mounted on top of the fan housing 23. The outlet or discharge from the scroll fan housing 23 is shown as being horizontally directed through an opening 33 through the bottom of the partition I6 into the chamber I8.

The combustion chamber shell 20 is shown as being of a vertically elongated box-like rectangular construction and as having a bottom wall 35, a front wall 36, a rear wall 3'1, side walls 38 and a top wall 39. At its upper end the combustion chamber is provided with a flue 40 which extends through an opening 4| in the top wall I5 of the casing I0 and can be sealed therein in any suitable manner as by a collar or ring 42.

The shell 20 of the combustion chamber is shown as supported on four legs 43, each pair of these legs being in the form of downward extensions of the ends of a cross piece 44 which cross piece is suitably secured to the under side of the bottom wall 35 of the combustion chamber shell 20. The lower end of each of these legs can be flanged inwardly, as indicated at 45, and

as secured to the bottom wall ll of the casing l by a bolt 46 or in any other suitable manner.

The legs 43 for the shell of the combustion chamber support the bottom wall 35 of the combustion chamber a substantial distance above the bottom wall ll of the casing l0 so as to provide a relatively high air inlet chamber 50 between the bottom walls 35 and H of the combus tion chamber shell 20 and easing 1'0, respectively, and which air inlet chamber 50 is in line with the lower part of the fan discharge 32 so as to receive air directly therefrom.

The combustion chamber shell 20 is also of smaller horizontal dimensions than the chamber la in which it is contained and its front, rear and side walls 36, 31 and 38 are spaced. respec tively, from the front wall l2, partition and side walls l4 of the casing It]. This spacing provides an air space 5| completely surrounding the combustion chamber shell '20 and through which the air discharged from the fan outlet 32 into the air inlet chamber 50 travels upwardly and escapes through the an outlet 53 of the casing 10. This air outlet is arranged to extend horizontally through the upper end of the front wall 12 of the casing ill. It is also desirable to space the top Wall 39 of the combustion chamber shell from the top wall I5 of the casing as shown;

The shell 20 of the combustion chamber is provided with a plurality of spaced passages or tubes 54 which are shown as being horizontal and are shown as supported at their opposite ends in the front and rear walls 36 and 31 of the combustion chamber shell and opening to the exterior thereof. The important feature of the invention resides in the provision or a reservoir, as hereinafter described, to provide a high velocity flow of air 'equally through all of these tubes These passages or 'tubes 54 are designed to carry a part of the air stream'at high velocity and preferably aline with the air outlet 53 of the casing 10. While the passages 54 are shown in the form of tubes, it is obvious that these passages could be of other form, as the form of internal or external passages cast integrally with the shell 20 of the combustion chamber, the essential function being that they provide for a restricted flow of the air, as compared with the space 51 thereby to effect a high velocity movement of the air throughout as hereinafter described The most important feature of the invention .resides providing high air pressure of equal value at the rear or inlet end of each of the passages or tubes 5s without penalizing or imposing undue back pressure on the relatively low pressure motor driven fan unit [9. To this end it will be noted that the upper part of the discharge32 from the .fan alines with the lower part ofthe rear wall 31 of the combus-tion chamber shell 20 so that a part of the air discharged by this motor driven fan unit I9 is forced to travel vertically upwardly through the space between the rear wall 31 of the combustion chamber shell 20 and the partition 16. This air is trapped at the upper end of this space by a hood indicated generally at 55 and which is shown as comprising a sheet metal par tition strip 56 and having depending sheet metal legs 58 at its opposite ends, the strip 56 being secured to the top wall 39 of the combustion chamber shell and the side legs 58 being secured to the side walls 38 of the combustion chamber shell. The partition strips 56 and 58 extend to the partition 16 so as to completely block the upper end of the space between the walls '31 and I6 and additionally the strip 56 and its side leg 58 can be connected by a rear wall 59- laying against the partition It as shown. The lower end of the hood 55 is open as indicated at 60 and hence this hood operates to trap the part of the stream of air forced upwardly through the space between the walls 31 and I6 by the motor driven blower unit I9 and hence create an air pressure within this hood which is very substantially higher than the air pressure in any part of the rest of the space 5| between the side walls of the combustion chamber shell 20 and the surrounding casing ID.

This high air pressure at the inlet ends of the passages-or tubes 54 serves to insure an equalized movement of air at high velocity through these passages or tubes,- each tube handling the same amount of air at the same pressure and velocity and this air being discharged from these tubes directly to the air outlet '53. Since the air passes at high velocity through the passages or tubes 54 a very high rate of heat transfer obtains between the products of combustion passing around these passages or tubes and the air so passing at high velocity through these passages or tubes. Accordingly high heat transfer efficiency is obtained, permitting of the extremely compact light weight structure shown, and resulting in low flue gas temperatures and overall heating efficiency. At the same time, this high velocity of the air passing through the passages or tubes 54 is obtained without requiring the use of a separate high pressure fan-or without even imposing any undue back pressure on the low pressure fan unit 19 shown.

The size of internal volume of the hood '55 has been found to be an important factor in the proper functioning of the hot air furnace. It has been found that the size or internal volume of this hood is in inverse ratio to the speed or size of the blower. With a slower speed blower, this hood 55 can be enlarged to include a part of the space between the side walls 38 and 14 of the combustion chamber shell 20 and enclosing casing I0 as well as a part-of the space between the top walls 39 and 15 thereof. It is essential that this hood 55 be proportioned in volume to the air supply and to the restriction afforded by the passages or tubes at which form the outlets from this hood in order to achieve optimum efficiency.

The combustion chamber shell 20 is provided with the usual inspection neck or passage 63 which extends forwardly through the front wall I2 of the casing iii and can be provided with the usual inspection door 64. The combustion chamber shell 26 is also shown as provided with the usual inlet passage or neck 55 for the insertion of the usual fuel burning apparatus (not shown), this neck 65 also extending through the front wall I2 of the casing. Immediately above the neck or passage 53 and immediately below the outlets of the tube 54, the combustion chamber shell 20 is also preferably provided with a forwardly projecting horizontal flange 66. It has been found that this flange 53 prevents the upwardly moving air in the space 5! between the front walls 42 and 36, of the casing H1 and combustion chamber shell 20, respectively, from interfering with the escape of air from the lowermost row of tubes 54. Without this flange 56 this interference was such as to result in occasional burning out of this lowermost row of tubes 54 due to the retarding of the flow of air therethrough In order to balance the impedance provided by these necks 63 and B5, fins 61 and the flange 36* are provided in the spaces between the side walls 88- of the combustion chamber shell and the side wall It of the surrounding casing. These fins can be of any suitable construction and are shown as being elongated upwardly inclining plates or strips extending fore and aft and having flanges 68 by means of which each of these fins can be attached to the inside of the corresponding side wall of the surrounding casing. In the air furnace shown, three of these fins 67 are provided at each side of the furnace and these are of such size as to balance the impedance provided by the necks 63 and 65 and flange 66, and with these parts 63, 65 and 66 to provide sufficient back pressure to balance the impedance provided by the passages or tubes 54 and the hood 55.

As previously indicated, the reservoir provided by the hood 55 can be made of any desired size and in Figs. 5 and 6 a modification is shown in which this reservoir is greatly enlarged. In this modification the hood i is provided by a pair of sheet metal partition strips ll each of which is of L-shape having an upper horizontal part 12 fitting between the top wall 39 of the combustion chamber shell 26, the top wall l of the housing or casing 10, the stack 40, and the corresponding side wall M of the housing or casing l9, and each partition strip also having a depending leg 18 which fits between the corresponding side walls l4 and 36 of the housing or casing l9 and the combustion chamber shell 20. To secure each of these L-shaped partition strips in place they are preferably marginally flanged, as indicated at is at the edges meeting the above walls and stack and these flanges can be secured to these walls and stack in any suitable manner. It will be seen that the reservoir 75 provided at the inlet ends of the tubes or passages 54 is greatly enlarged as compared with that shown in Figs. 1-4.

From the foregoing it will be seen that the present invention provides a very compact, light weight air furnace having a high capacity and efiiciency and which in particular is obtained by the entrapment of a part of a stream of air delivered by a low pressure blower so as to create an equalized high inlet pressure for each of a series of tubes extending either horizontally or vertically through the combustion chamber and thereby provide a very high velocity of the air passing through these tubes as compared with the balance of the air which passes around the exterior walls of the combustion chamber. It will further be seen that this high velocity of the air passing through the tubes is achieved from a low pressure fan without undue back pressure and that the desired balance of the movement of air through all parts of the furnace can be readily adjusted.

While the foregoing describes a specific embodiment of the invention, the essential feature of the invention, as summarized in the accompanying claims, resides in the entrainment of a part of the air from a low pressure fan to create a high equalized pressure of air at the inlet end of a series of heat transfer passages or tubes to obtain an equalized high velocity of air passing therethrough.

I claim:

1. A hot air furnace, comprising a vertically elongated sheet metal combustion chamber shell having top and bottom walls and having at least one of its side walls in the form of a vertical generally flat wall, a sheet metal casing surrounding said combustion chamber with top, bottom and side walls in spaced relation to the corresponding walls of said combustion chamber sheli and generally conforming thereto to have a vertical generally flat wall arranged generally parallel and spaced from said vertical generally flat wall of said combustion chamber shell, an air inlet through the lower part of said vertical generally fiat wall of said casing and having its lower part in line with the space below the bottom wall of said combustion chamber shell and having its upper part in line with the lower end of said vertical generally flat wall of said combustion chamber whereby air from said air inlet is divided into one stream striking said vertical generally flat wall of said combustion chamber and flowing upwardly between said vertical generally flat walls of said combustion chamber shell and casing and into another stream flowing horizontally into the space under the bottom wall of said combustion chamber shell and thence upwardly between the other side walls of said combustion chamber shell and easing, a blower arranged to discharge air into said air inlet, an air outlet through the upper part of the side wall of said casing opposite the vertical generally flat wall thereof and relieving air from the space between said combustion chamber shell and casing, horizontal spaced tubes extending in line with said air outlet from said vertical generally flat wall of said combustion chamber shell to the opposite side wall thereof and opening to the exterior of said combustion chamber shell, the free area through said tubes being very substantially less than the free area through the space between the side walls of said combustion chamber shell and casing whereby said tubes provide a relatively restricted path for air flow, and a partition forming with said vertical generally flat wall of said combustion chamber shell a hood across the upper part of the space between said vertical generally fiat walls of said combustion chamber shell and casing and said hood enclosing the corresponding inlet ends of said tubes, said hood being open toward said air inlet .to receive, confine and direct said first stream of air through said tubes at a velocity substantially greater than any part of said second stream of air.

2. A structure as set forth in claim 1 wherein a horizontal flange projects outwardly from said opposite side wall of said combustion chamber shell immediately below the outlet ends of said tubes part way across the space between said combustion chamber shell and casing to deflect the second stream of air flowing upwardly through said last space and toward said air outlet away from said outlet ends of said tubes.

HARRY S. MURPHY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,089,407 Norris Aug. 10, 1937 2,109,876 Bard Mar. 1, 1938 2,181,617 Ashley Nov. 28, 1939 2,283,407 Bassett May 19, 1942 2,299,901 Johnston Oct. 27, 1942 2,474,090 Carter June 21, 1949 FOREIGN PATENTS Number Country Date 859,169 France May 27, 1940 

